1. Field of the Invention
The invention relates to a composite foil having at least two layers in which at least one cover or sealing layer which is normally insoluble in water, is connected to a water-soluble reaction material of at least one layer, which contains a dissolving intermediary for the sealing cover layer. The cover layer is made free from pores by its extrusion as a foil of thermoplastic material.
2. Description of the Prior Art
U.S. Pat. No. 4,261,066 (corresponding to German Offenlegungsscrift 2 703 005) in the Applicant's name, discloses a foil adapted to be used once by being laid on a toilet seat. In one embodiment the foil can take the form of a composite foil, a water-soluble layer being turned towards the user and the foil having on its side remote from the user a cover or sealing layer insoluble in water. This cover layer can be dissolved in an acid or basic medium. To cause such dissolving, the water-soluble layer contains a corresponding basic or acid additive, so that when immersed in water the foil is soluble as a whole, but the composite foil is not caused to dissolve when water contacts only its cover layer. The soluble layer is fibrous textile waste and the seal layer is synthetic material such as polyvinyl alcohol, applied very thinly by wetting the soluble layer with a dilute solution thereof in solvent, and evaporating away the solvent to leave the seal layer.
The described solvent-carried-solids method is rather complex and has certain drawbacks, such as the use of difficult to handle solvents and the need for equipment to accomplish the evaporating. Moreover, the resulting product is not entirely acceptable because pores form upon evaporating the solvent that detract from the basic function of the sealing layer, namely to prevent ingress of moisture to the reaction layer.
Parent copending application Ser. No. 645,508 (corresponding to European Patent Application 80 108 243.9), also in the Applicant's name, is directed to a further development of this toilet seat covering and mentions that such a composite foil is also suitable as a packing material and for the making of carrier bags, sachets and the like.
The foil of the kind disclosed in this latter application is extremely suitable for many applications. The sealing and reaction layers can be formed as before, but preferably they are pre-formed flat sheets by joined adhesive bonding or welding, for example dissolving the surface of the layer prior to bonding. Preferably, this foil comprises two layers of the same plastics material, but only one of them (i.e., the reaction layer) contains the solubilizers that dissolve both layers of the plastics material when exposed to water.
The foil of this general type has now also been found to be particularly useful as a packing material, not only in flexible form, but also in self-supporting form, more particularly in the form of semi-rigid to rigid sheets. Mechanical support capacity and rigidity can be achieved if the polymers of the reaction and/or cover layer are themselves formulated of rigid material or the reaction layer and/or the cover layer are provided with fillers, more particularly mineral fillers and/or fibrous material. In this manner, the reaction layer of the composite foil can be constructed in the same structures as found in packings made of paper, cardboard, pasteboard or corrugated pasteboard. The binder used in the structures is water-soluble or dissolvable by the dissolving intermediary which is contained in the reaction layer, and the dissolving intermediary preferably is effective to cause dissociation of the cover layer. Furthermore, the reaction layer, as done in papermaking, can be produced by accumulating a sediment of the components from aqueous solution in an alkaline or acid medium. The finished composite foil can therefore take conventional forms of blanks for packing material, for example being pre-punched or provided with embossed lines for subsequent folding. The foil can also be pre-shaped into boxes, if necessary with lids. The composite foil is particularly suitable as a packing for items such as cigarettes and other goods whose packaging is frequently thrown away carelessly by consumers and will contaminate the environment, unless it dissolves or rots away quickly.
In one embodiment of the present invention, composite foil is printed on, more particularly in colors. Even use of the foil as an information medium or handbill causes no permanent environmental contamination because even if the packing material is simply thrown away by the consumer, it quickly decomposes upon penetration of moisture. If the reaction layer is produced separately from the cover layer, and since the reaction layer is preferably to be printed on, the capacity to function as a print medium can be aided or the printing process facilitated by the use of suitable fillers in the reaction layer.